Try Intel Macos 15

.github/workflows/mac-builds.yml

@@ -4,13 +4,11 @@ on: [push, pull_request]
 
 jobs:
   build:
-    # From macos-14 forward, the baseline "macos-X" image is Arm based,
-    # and not Intel based.
     runs-on: ${{matrix.image}}
     strategy:
       fail-fast: false
       matrix:
-        image: [macos-13, macos-14, macos-15]
+        image: [macos-15, macos-15-intel]
         build_type: [Debug, Release]
         std: [14, 17]